Thomas is an attacker and he skimmed through the HTML source code of an online shopping website for the presence of any vulnerabilities that he can exploit.
He already knows that when a user makes any selection of items in the online shopping webpage, the selection is typically stored as form field values and sent to the application as an HTTP request (GET or POST) after clicking the Submit button. He also knows that some fields related to the selected items are modifiable by the user (like quantity, color, etc.) and some are not (like price). While skimming through the HTML code, he identified that the price field values of the items are present in the HTML code. He modified the price field values of certain items from $200 to $2 in the HTML code and submitted the request successfully to the application.
Identify the type of attack performed by Thomas on the online shopping website?